Do My Microbes Love You? How Your Bacteria Affect Your Love Life

Microbiology Today

February 14, 2020

In November, we explored how our microbes have a tremendous influence on our nutrition, immunity, and overall well-being. In honor of Valentine’s Day, we take a more in-depth look into the many ways our microbes impact us in a seemingly unlikely area — our love life. Is it more accurate to say a couple have “Good Microbiology” rather than to say a couple has “Good Chemistry”?

Few things in human behavior are as ubiquitous as kissing. Nearly every human culture throughout history includes kissing loved ones. When you think about it, kissing is a strange behavior that carries a great deal of risk of passing contagions for both parties. New research suggests that the contagious aspect of kissing might be the reason we evolved the behavior in the first place.

Animals that form social groups, like humans, share pathogens and parasites from close contact like kissing. However, we also share the far more prevalent health-promoting microbes as well. Most bacteria we share in a kiss are beneficial, and even help bolster our metabolism and immunity. Some scientists believe that the need to share these benefits may be the origin of social groups in the animal kingdom.

A kiss might also have evolved as a crude form of vaccination against harmful microbes. Humans carry many chronic pathogens that can injure a fetus in the womb. Many scientists believe that one significant benefit to romantic kissing is so that the mother can be exposed to the father’s potentially harmful microbes and develop immunity against them before pregnancy.

Bacteria also might play a role in relationship matchmaking. Numerous studies have shown that people can subconsciously sense the others’ immune system genes by scent. One famous Swiss study asked women to rate the attractiveness of a potential partner by smelling their dirty t-shirts. The women did not agree on which smells were the most attractive. Instead, they most often preferred the t-shirt of the man that had the most complimentary immune system that would broaden their offspring’s spectrum of immunity [i].

The strange thing is that the immune genes and resulting sweat don’t have much of a smell. Instead, a person’s body odor comes from the specific microbes that consume their sweat, skin cells, and oils. So the women smelling the dirty t-shirts were not smelling the men’s immune system genes directly, but they could sense the small differences that the immune system had on the type of microbes that grew.

Susan Erdman, a microbiologist at M.I.T., recently made a surprising discovery about how the desire to be connected to others and to have companionship may have another microbial component. During an experiment, Dr. Erdman changed the diets of her mice to probiotic food. Over the next few weeks, she was surprised to find that the probiotic raised the levels of an important hormone called oxytocin [ii]. Often called ‘the love hormone,’ Oxytocin helps us bond with one another. Our bodies release it when we kiss, breast-feed, and even just when people hang out with close friends. It is a hormone that helps us create bonds with partners and our children.

The mice also seemed a great deal healthier in general and had what Dr. Erdman called an unusual “glow of health.” The mice grew unusually thick fur, developed more confident behavior, among other benefits [iii]. “They simply looked far healthier than before,” she said, “it seems that their elevated gut microbes had transformed these animals into rodent sweethearts.” The same health benefits between humans and gut microbiome are still yet to be fully proven, but Dr. Erdman suggests that the microbes you harbor can make your skin smooth and your hair healthy; they may even put a spring in your step.

As the science around our microbiota continues to evolve, we begin to see just how profoundly important our bacteria are in our daily lives — even in surprising areas of our lives. It is a startling fact that there are as many microbes in your body as human cells [iv]. Bacteria have evolved along with us since the dawn of time, and the more we learn, the more we begin to see that the microbes are a mutual partner in life. Another way to look at it: by making their hosts match with and look well to a possible partner, microbes help to ensure their own continued existence. When it comes to our beneficial bacteria, everyone wins!

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  1. Wedekind C, Seebeck T, Bettens F, Paepke AJ. 1995Data from: MHC-dependent mate preferences in humans. Dryad Digital Repository. (doi:10.5061/dryad.r87pq) Accessed 10 Feb 2020.
  2. Erdman, S.E. & Poutahidis, Theofilos. (2016). Microbes and Oxytocin: Benefits for Host Physiology and Behavior. 10.1016/bs.irn.2016.07.004. Accessed 10 Feb 2020. Accessed 10 Feb 2020.
  3. Levkovich, Tatiana et al. “Probiotic bacteria induce a ‘glow of health’.” PloS one vol. 8,1 (2013): e53867. doi:10.1371/journal.pone.0053867. Accessed 10 Feb 2020.
  4. Sender R, Fuchs S, Milo R. Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biol. 2016;14(8):e1002533. Published 2016 Aug 19. doi:10.1371/journal.pbio.1002533. Accessed 10 Feb 2020.